It is known in the art that prior to the application of protective coatings on a surface, it is necessary to determine if the surface is free of contaminants, and in particular, soluble salt contaminants. Contaminants that are not removed prior to the application of a protective coating can lead to the failure of the protective coating and corrosion of the surface to be protected. For example, soluble salts on a metal surface can cause adhesion problems due to the hygroscopic nature of salt which attracts water through the permeable protective coating, resulting in a build-up of water molecules between the surface and the coating. This results in the creation of osmotic pressure, the creation of an electrolytic cell, and ultimately causes corrosion of the surface. It is particularly important to determine if soluble salt contaminants exist on the surface so that attempts to clean the surface before coating do not inadvertently embed contaminants into the surface material. Furthermore, performance standards for protective coatings typically define the allowable concentration of soluble salts so it is important to determine the concentration of such salts on the surface prior to application of the protective coating.
To test for the presence of contaminants, chemical reaction tests that provide colored indications as to the concentration of soluble solvents in a solution have been devised, along with conductivity measurement tests. Multiple techniques for collecting samples from a surface have also been developed including swabbing, boiling, using a test sleeve, and using as Bresle patch.
Swabbing relies on using a cotton swab soaked in a measured amount of solution. A measured area of the contaminated surface is brushed with a damp cotton swab. The damp cotton swab is swirled in the solution and squeezed. This process is repeated several times with new cotton swabs, and each time the cotton swabs are left in the solution. Finally, a fresh cotton swab is then used to dry the surface and is also deposited in the solution. The solution with the cotton swabs is stirred for several minutes, and the concentration of salt is then measured. The disadvantage of the swabbing method is that it is labor intensive, and subject to contamination from the swabs, the user's hands, and tweezers used for swabbing. The measurement may also be inaccurate due to a failure to retain all of the test solution, especially on sloped or overhead surfaces.
Boiling involves taking a sample of the contaminated surface into a laboratory and boiling it in a measured volume of deionized water for one hour. The concentration of salt in the test solution is then measured. The involvement of the laboratory is a disadvantage of this method, as is the requirement that a sample of the surface must be removed from the job site. Like the swiping method, contamination is possible, either from prior tests or from contaminations in the boiled water.
The test sleeve method involves a cylindrical latex sleeve with a dosed end and an open end with an adhesive ring. The test sleeve is filled with a measured amount of water which collects at the closed end of the sleeve. The adhesive ring at the open end of the sleeve is then placed in contact with the surface to be measured, and the closed end of the sleeve is raised. The measured amount of water flows to the open end of the sleeve and makes contact with the surface to be measured. The test sleeve is then agitated to help the water dissolve the contaminants on the surface. The closed end is then lowered to allow the solution to flow as from the surface at the open end of the test sleeve. The sleeve is then removed from the surface and the solution measured. This method is difficult to employ on horizontal surfaces since gravity pulls the solution towards the open end of the test sleeve, complicating removal of the sleeve and retention of the test solution. It can also be difficult to remove the solution from the test sleeve after it has been removed from the surface.
The Bresle patch method starts with a dry portion of the metallic surface with no rust, dirt, or moisture so that a patch frame with an adhesive may be applied to the metallic surface. The Bresle patch is then applied onto the metallic surface with adhesive to form a tight seal. Typically, the patch is a latex sheet with a double-sided adhesive foam ring on one side. A sampling chamber is formed between the latex and the metallic surface enclosed by the foam ring. Ideally, the Bresle patch will be applied in a manner so that little air is sealed within the patch. The characteristics of a certain amount of deionized water are then measured prior to injection into the Bresle patch so that a baseline may be established. This same amount of deionized water is then injected into the Bresle patch and agitated by the user so that any soluble salts on the metallic surface are dissolved in the deionized water. Typically, the latex sheet accommodates the injected deionized water through its elasticity. The deionized water may also be removed and reinjected into the Bresle patch to further dissolve any soluble salts. The deionized water is then collected from the Bresle patch and measured. The difference between the second and first measured value represents the level of contamination on the surface.
Although the Bresle method is popular, there are disadvantages. The patch used in the Bresle method relies on an adhesive to attach to the surface to be measured. This adhesive can fail to create a watertight seal in situations where, for example, the surface is heavily pitted, the surface has been blasted by particles in an attempt to clean the surface, and the surface is curved. The adhesive can also leave behind a residue, further contaminating the surface. The patches may also contain contaminants and therefore distort measurements. The single-use nature of the patches generates waste and increases the cost of the test. The requirement for a needle is another disadvantage associated with the Bresle method. A sharp needle capable of piercing the latex and the foam adhesive of the patch is also capable of injuring the user. On some job sites, the sharp needle is sufficient to complicate or limit the adoption of the Bresle method. The process of penetrating through the latex and adhesive foam while maintaining a watertight seal can also be challenging. The need to measure samples of the water both before and after injection into the patch complicates this method as well, and also creates an additional opportunity for contamination. It is also necessary to remove all of the water deposited into a conductivity meter during the pre-measurement reading or the amount of water injected into the patch may be incorrect. Other steps that are typically performed may also provide opportunities for contamination. For example, users will often meter out more water than is necessary into the syringe, and inject some of this water into the conductivity meter prior to pre-measurement. The water is then discarded from the meter and from the syringe until the syringe has the desired volume. This additional step that is not strictly necessary to the performance of the Bresle method introduces the opportunity for contamination if the conductivity meter is not properly cleaned.
These and other deficiencies in known methods of testing for contaminants on a surface are addressed by the method and system described here.